[Clang] Use env to set variable in config-file3.c

There was an earlier patch that was supposed to fix this up that
apparently did not get to everything. After this patch, the test passes
inside the internal shell.

Author: boomanaiden154

clang/test/Driver/config-file3.c

@@ -230,7 +230,7 @@
 
 //--- Tilde expansion in user configuration file directory
 //
-// RUN: HOME=%S/Inputs/config %clang -### --config-user-dir=~ -v 2>&1 | FileCheck %s --check-prefix=CHECK-TILDE
+// RUN: env HOME=%S/Inputs/config %clang -### --config-user-dir=~ -v 2>&1 | FileCheck %s --check-prefix=CHECK-TILDE
 // CHECK-TILDE: User configuration file directory: {{.*}}/Inputs/config
 
 //--- Fallback to stripping OS versions